Devil's herb

If inhaling the vapors of this plant is enough to cause slight hallucinations for a few hours, it's by ingestion that it becomes a real poison that causes strong hallucinations and a loss of voice.
A creature that is subjected to this poison succeed on a DC 10 Constitution DC 10 saving throw or suffer hallucinations and not be able to speak intelligibly until it finishes a long rest. At the end of the long rest the creature has no memory of what happened since it takes the poison.